This is what the ignition looks like after being modified to
look like the pre-1983 wiring. This modification to later CJs was made famous on the Internet most notably
by John Nutter, and is commonly referred to as
"The Nutter Bypass,"
or "The Nutter Mod."
The solid-state ignition module is located
under the washer reservoir.
A length of wire must be
added to extend the violet wire from the distributor to
the ignition module.
The distributor vacuum advance hose is moved from
manifold vacuum to ported vacuum. You should add a tee
here because ported vacuum also operates the EGR valve and charcoal canister purging.
The stepper motor on the Carter BBD is unplugged. The metering pins should be moved
forward to the full-rich position before
unplugging it. To accomplish this, and assuming the stepper motor is working to begin with:
- Create an air leak somewhere by unplugging a vacuum line.
The metering pins should move forward to the full-rich position.
- Turn the engine off.
- Unplug the stepper motor.
There is discussion and disagreement about whether the metering pins should be fully forward, or
more toward the middle. In my own personal experience, placing them fully forward makes the engine
run a little stronger, but placing them more toward the middle improves gas mileage somewhat.
The timing must be set differently since the computer no longer controls it.
- Disconnect the vacuum advance hose at the distributor and plug it.
- Set the timing to 8 degrees BTDC.
- Reconnect the vacuum hose.
Your buddy borrowed your timing light and never
returned it? Here's a trick I learned from my brother. The timing
can be set to surprising accuracy with a vacuum gauge. Hook the
gauge to manifold vacuum and run the engine at curb idle. Rotate
the distributor clockwise to retard the timing. Now slowly rotate
it counter-clockwise to the point where you just
reach the maximum vacuum reading. Back off (clockwise) until the
vacuum drops by 1". Lock the distributor down. Timing can be
set to ±1° using this method.
With no distributor signal input, the computer does
not know the engine is running, and remains asleep. In
this state, the input sensors and controlled devices have
no function. The idle speed controls, BBD stepper motor, and the Pulse Air
system do not work.
Looking at it another way, if the computer has been taken out of the loop and no longer functions,
the only things that do
- The Decel Valve
- The air doors in the air cleaner snorkel
- The EGR Valve
- The Evaporation Canister
- The Electric Choke
- The Manifold Heater
- The PCV System